yading@11: /*
yading@11:  * SRTP encryption/decryption
yading@11:  * Copyright (c) 2012 Martin Storsjo
yading@11:  *
yading@11:  * This file is part of FFmpeg.
yading@11:  *
yading@11:  * FFmpeg is free software; you can redistribute it and/or
yading@11:  * modify it under the terms of the GNU Lesser General Public
yading@11:  * License as published by the Free Software Foundation; either
yading@11:  * version 2.1 of the License, or (at your option) any later version.
yading@11:  *
yading@11:  * FFmpeg is distributed in the hope that it will be useful,
yading@11:  * but WITHOUT ANY WARRANTY; without even the implied warranty of
yading@11:  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
yading@11:  * Lesser General Public License for more details.
yading@11:  *
yading@11:  * You should have received a copy of the GNU Lesser General Public
yading@11:  * License along with FFmpeg; if not, write to the Free Software
yading@11:  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
yading@11:  */
yading@11: 
yading@11: #include "libavutil/base64.h"
yading@11: #include "libavutil/aes.h"
yading@11: #include "libavutil/hmac.h"
yading@11: #include "libavutil/intreadwrite.h"
yading@11: #include "libavutil/log.h"
yading@11: #include "rtp.h"
yading@11: #include "rtpdec.h"
yading@11: #include "srtp.h"
yading@11: 
yading@11: void ff_srtp_free(struct SRTPContext *s)
yading@11: {
yading@11:     if (!s)
yading@11:         return;
yading@11:     av_freep(&s->aes);
yading@11:     if (s->hmac)
yading@11:         av_hmac_free(s->hmac);
yading@11:     s->hmac = NULL;
yading@11: }
yading@11: 
yading@11: static void encrypt_counter(struct AVAES *aes, uint8_t *iv, uint8_t *outbuf,
yading@11:                             int outlen)
yading@11: {
yading@11:     int i, j, outpos;
yading@11:     for (i = 0, outpos = 0; outpos < outlen; i++) {
yading@11:         uint8_t keystream[16];
yading@11:         AV_WB16(&iv[14], i);
yading@11:         av_aes_crypt(aes, keystream, iv, 1, NULL, 0);
yading@11:         for (j = 0; j < 16 && outpos < outlen; j++, outpos++)
yading@11:             outbuf[outpos] ^= keystream[j];
yading@11:     }
yading@11: }
yading@11: 
yading@11: static void derive_key(struct AVAES *aes, const uint8_t *salt, int label,
yading@11:                        uint8_t *out, int outlen)
yading@11: {
yading@11:     uint8_t input[16] = { 0 };
yading@11:     memcpy(input, salt, 14);
yading@11:     // Key derivation rate assumed to be zero
yading@11:     input[14 - 7] ^= label;
yading@11:     memset(out, 0, outlen);
yading@11:     encrypt_counter(aes, input, out, outlen);
yading@11: }
yading@11: 
yading@11: int ff_srtp_set_crypto(struct SRTPContext *s, const char *suite,
yading@11:                        const char *params)
yading@11: {
yading@11:     uint8_t buf[30];
yading@11: 
yading@11:     ff_srtp_free(s);
yading@11: 
yading@11:     // RFC 4568
yading@11:     if (!strcmp(suite, "AES_CM_128_HMAC_SHA1_80") ||
yading@11:         !strcmp(suite, "SRTP_AES128_CM_HMAC_SHA1_80")) {
yading@11:         s->rtp_hmac_size = s->rtcp_hmac_size = 10;
yading@11:     } else if (!strcmp(suite, "AES_CM_128_HMAC_SHA1_32")) {
yading@11:         s->rtp_hmac_size = s->rtcp_hmac_size = 4;
yading@11:     } else if (!strcmp(suite, "SRTP_AES128_CM_HMAC_SHA1_32")) {
yading@11:         // RFC 5764 section 4.1.2
yading@11:         s->rtp_hmac_size  = 4;
yading@11:         s->rtcp_hmac_size = 10;
yading@11:     } else {
yading@11:         av_log(NULL, AV_LOG_WARNING, "SRTP Crypto suite %s not supported\n",
yading@11:                                      suite);
yading@11:         return AVERROR(EINVAL);
yading@11:     }
yading@11:     if (av_base64_decode(buf, params, sizeof(buf)) != sizeof(buf)) {
yading@11:         av_log(NULL, AV_LOG_WARNING, "Incorrect amount of SRTP params\n");
yading@11:         return AVERROR(EINVAL);
yading@11:     }
yading@11:     // MKI and lifetime not handled yet
yading@11:     s->aes  = av_aes_alloc();
yading@11:     s->hmac = av_hmac_alloc(AV_HMAC_SHA1);
yading@11:     if (!s->aes || !s->hmac)
yading@11:         return AVERROR(ENOMEM);
yading@11:     memcpy(s->master_key, buf, 16);
yading@11:     memcpy(s->master_salt, buf + 16, 14);
yading@11: 
yading@11:     // RFC 3711
yading@11:     av_aes_init(s->aes, s->master_key, 128, 0);
yading@11: 
yading@11:     derive_key(s->aes, s->master_salt, 0x00, s->rtp_key, sizeof(s->rtp_key));
yading@11:     derive_key(s->aes, s->master_salt, 0x02, s->rtp_salt, sizeof(s->rtp_salt));
yading@11:     derive_key(s->aes, s->master_salt, 0x01, s->rtp_auth, sizeof(s->rtp_auth));
yading@11: 
yading@11:     derive_key(s->aes, s->master_salt, 0x03, s->rtcp_key, sizeof(s->rtcp_key));
yading@11:     derive_key(s->aes, s->master_salt, 0x05, s->rtcp_salt, sizeof(s->rtcp_salt));
yading@11:     derive_key(s->aes, s->master_salt, 0x04, s->rtcp_auth, sizeof(s->rtcp_auth));
yading@11:     return 0;
yading@11: }
yading@11: 
yading@11: static void create_iv(uint8_t *iv, const uint8_t *salt, uint64_t index,
yading@11:                       uint32_t ssrc)
yading@11: {
yading@11:     uint8_t indexbuf[8];
yading@11:     int i;
yading@11:     memset(iv, 0, 16);
yading@11:     AV_WB32(&iv[4], ssrc);
yading@11:     AV_WB64(indexbuf, index);
yading@11:     for (i = 0; i < 8; i++) // index << 16
yading@11:         iv[6 + i] ^= indexbuf[i];
yading@11:     for (i = 0; i < 14; i++)
yading@11:         iv[i] ^= salt[i];
yading@11: }
yading@11: 
yading@11: int ff_srtp_decrypt(struct SRTPContext *s, uint8_t *buf, int *lenptr)
yading@11: {
yading@11:     uint8_t iv[16] = { 0 }, hmac[20];
yading@11:     int len = *lenptr;
yading@11:     int av_uninit(seq_largest);
yading@11:     uint32_t ssrc, av_uninit(roc);
yading@11:     uint64_t index;
yading@11:     int rtcp, hmac_size;
yading@11: 
yading@11:     // TODO: Missing replay protection
yading@11: 
yading@11:     if (len < 2)
yading@11:         return AVERROR_INVALIDDATA;
yading@11: 
yading@11:     rtcp = RTP_PT_IS_RTCP(buf[1]);
yading@11:     hmac_size = rtcp ? s->rtcp_hmac_size : s->rtp_hmac_size;
yading@11: 
yading@11:     if (len < hmac_size)
yading@11:         return AVERROR_INVALIDDATA;
yading@11: 
yading@11:     // Authentication HMAC
yading@11:     av_hmac_init(s->hmac, rtcp ? s->rtcp_auth : s->rtp_auth, sizeof(s->rtp_auth));
yading@11:     // If MKI is used, this should exclude the MKI as well
yading@11:     av_hmac_update(s->hmac, buf, len - hmac_size);
yading@11: 
yading@11:     if (!rtcp) {
yading@11:         int seq = AV_RB16(buf + 2);
yading@11:         uint32_t v;
yading@11:         uint8_t rocbuf[4];
yading@11: 
yading@11:         // RFC 3711 section 3.3.1, appendix A
yading@11:         seq_largest = s->seq_initialized ? s->seq_largest : seq;
yading@11:         v = roc = s->roc;
yading@11:         if (seq_largest < 32768) {
yading@11:             if (seq - seq_largest > 32768)
yading@11:                 v = roc - 1;
yading@11:         } else {
yading@11:             if (seq_largest - 32768 > seq)
yading@11:                 v = roc + 1;
yading@11:         }
yading@11:         if (v == roc) {
yading@11:             seq_largest = FFMAX(seq_largest, seq);
yading@11:         } else if (v == roc + 1) {
yading@11:             seq_largest = seq;
yading@11:             roc = v;
yading@11:         }
yading@11:         index = seq + (((uint64_t)v) << 16);
yading@11: 
yading@11:         AV_WB32(rocbuf, roc);
yading@11:         av_hmac_update(s->hmac, rocbuf, 4);
yading@11:     }
yading@11: 
yading@11:     av_hmac_final(s->hmac, hmac, sizeof(hmac));
yading@11:     if (memcmp(hmac, buf + len - hmac_size, hmac_size)) {
yading@11:         av_log(NULL, AV_LOG_WARNING, "HMAC mismatch\n");
yading@11:         return AVERROR_INVALIDDATA;
yading@11:     }
yading@11: 
yading@11:     len -= hmac_size;
yading@11:     *lenptr = len;
yading@11: 
yading@11:     if (len < 12)
yading@11:         return AVERROR_INVALIDDATA;
yading@11: 
yading@11:     if (rtcp) {
yading@11:         uint32_t srtcp_index = AV_RB32(buf + len - 4);
yading@11:         len -= 4;
yading@11:         *lenptr = len;
yading@11: 
yading@11:         ssrc = AV_RB32(buf + 4);
yading@11:         index = srtcp_index & 0x7fffffff;
yading@11: 
yading@11:         buf += 8;
yading@11:         len -= 8;
yading@11:         if (!(srtcp_index & 0x80000000))
yading@11:             return 0;
yading@11:     } else {
yading@11:         int ext, csrc;
yading@11:         s->seq_initialized = 1;
yading@11:         s->seq_largest     = seq_largest;
yading@11:         s->roc             = roc;
yading@11: 
yading@11:         csrc = buf[0] & 0x0f;
yading@11:         ext  = buf[0] & 0x10;
yading@11:         ssrc = AV_RB32(buf + 8);
yading@11: 
yading@11:         buf += 12;
yading@11:         len -= 12;
yading@11: 
yading@11:         buf += 4 * csrc;
yading@11:         len -= 4 * csrc;
yading@11:         if (len < 0)
yading@11:             return AVERROR_INVALIDDATA;
yading@11: 
yading@11:         if (ext) {
yading@11:             if (len < 4)
yading@11:                 return AVERROR_INVALIDDATA;
yading@11:             ext = (AV_RB16(buf + 2) + 1) * 4;
yading@11:             if (len < ext)
yading@11:                 return AVERROR_INVALIDDATA;
yading@11:             len -= ext;
yading@11:             buf += ext;
yading@11:         }
yading@11:     }
yading@11: 
yading@11:     create_iv(iv, rtcp ? s->rtcp_salt : s->rtp_salt, index, ssrc);
yading@11:     av_aes_init(s->aes, rtcp ? s->rtcp_key : s->rtp_key, 128, 0);
yading@11:     encrypt_counter(s->aes, iv, buf, len);
yading@11: 
yading@11:     return 0;
yading@11: }
yading@11: 
yading@11: int ff_srtp_encrypt(struct SRTPContext *s, const uint8_t *in, int len,
yading@11:                     uint8_t *out, int outlen)
yading@11: {
yading@11:     uint8_t iv[16] = { 0 }, hmac[20];
yading@11:     uint64_t index;
yading@11:     uint32_t ssrc;
yading@11:     int rtcp, hmac_size, padding;
yading@11:     uint8_t *buf;
yading@11: 
yading@11:     if (len < 8)
yading@11:         return AVERROR_INVALIDDATA;
yading@11: 
yading@11:     rtcp = RTP_PT_IS_RTCP(in[1]);
yading@11:     hmac_size = rtcp ? s->rtcp_hmac_size : s->rtp_hmac_size;
yading@11:     padding = hmac_size;
yading@11:     if (rtcp)
yading@11:         padding += 4; // For the RTCP index
yading@11: 
yading@11:     if (len + padding > outlen)
yading@11:         return 0;
yading@11: 
yading@11:     memcpy(out, in, len);
yading@11:     buf = out;
yading@11: 
yading@11:     if (rtcp) {
yading@11:         ssrc = AV_RB32(buf + 4);
yading@11:         index = s->rtcp_index++;
yading@11: 
yading@11:         buf += 8;
yading@11:         len -= 8;
yading@11:     } else {
yading@11:         int ext, csrc;
yading@11:         int seq = AV_RB16(buf + 2);
yading@11: 
yading@11:         if (len < 12)
yading@11:             return AVERROR_INVALIDDATA;
yading@11: 
yading@11:         ssrc = AV_RB32(buf + 8);
yading@11: 
yading@11:         if (seq < s->seq_largest)
yading@11:             s->roc++;
yading@11:         s->seq_largest = seq;
yading@11:         index = seq + (((uint64_t)s->roc) << 16);
yading@11: 
yading@11:         csrc = buf[0] & 0x0f;
yading@11:         ext = buf[0] & 0x10;
yading@11: 
yading@11:         buf += 12;
yading@11:         len -= 12;
yading@11: 
yading@11:         buf += 4 * csrc;
yading@11:         len -= 4 * csrc;
yading@11:         if (len < 0)
yading@11:             return AVERROR_INVALIDDATA;
yading@11: 
yading@11:         if (ext) {
yading@11:             if (len < 4)
yading@11:                 return AVERROR_INVALIDDATA;
yading@11:             ext = (AV_RB16(buf + 2) + 1) * 4;
yading@11:             if (len < ext)
yading@11:                 return AVERROR_INVALIDDATA;
yading@11:             len -= ext;
yading@11:             buf += ext;
yading@11:         }
yading@11:     }
yading@11: 
yading@11:     create_iv(iv, rtcp ? s->rtcp_salt : s->rtp_salt, index, ssrc);
yading@11:     av_aes_init(s->aes, rtcp ? s->rtcp_key : s->rtp_key, 128, 0);
yading@11:     encrypt_counter(s->aes, iv, buf, len);
yading@11: 
yading@11:     if (rtcp) {
yading@11:         AV_WB32(buf + len, 0x80000000 | index);
yading@11:         len += 4;
yading@11:     }
yading@11: 
yading@11:     av_hmac_init(s->hmac, rtcp ? s->rtcp_auth : s->rtp_auth, sizeof(s->rtp_auth));
yading@11:     av_hmac_update(s->hmac, out, buf + len - out);
yading@11:     if (!rtcp) {
yading@11:         uint8_t rocbuf[4];
yading@11:         AV_WB32(rocbuf, s->roc);
yading@11:         av_hmac_update(s->hmac, rocbuf, 4);
yading@11:     }
yading@11:     av_hmac_final(s->hmac, hmac, sizeof(hmac));
yading@11: 
yading@11:     memcpy(buf + len, hmac, hmac_size);
yading@11:     len += hmac_size;
yading@11:     return buf + len - out;
yading@11: }
yading@11: 
yading@11: #ifdef TEST
yading@11: #include <stdio.h>
yading@11: 
yading@11: static const char *aes128_80_key = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmn";
yading@11: 
yading@11: static const uint8_t rtp_aes128_80[] = {
yading@11:     // RTP header
yading@11:     0x80, 0xe0, 0x12, 0x34, 0x12, 0x34, 0x56, 0x78, 0x12, 0x34, 0x56, 0x78,
yading@11:     // encrypted payload
yading@11:     0x62, 0x69, 0x76, 0xca, 0xc5,
yading@11:     // HMAC
yading@11:     0xa1, 0xac, 0x1b, 0xb4, 0xa0, 0x1c, 0xd5, 0x49, 0x28, 0x99,
yading@11: };
yading@11: 
yading@11: static const uint8_t rtcp_aes128_80[] = {
yading@11:     // RTCP header
yading@11:     0x81, 0xc9, 0x00, 0x07, 0x12, 0x34, 0x56, 0x78,
yading@11:     // encrypted payload
yading@11:     0x8a, 0xac, 0xdc, 0xa5, 0x4c, 0xf6, 0x78, 0xa6, 0x62, 0x8f, 0x24, 0xda,
yading@11:     0x6c, 0x09, 0x3f, 0xa9, 0x28, 0x7a, 0xb5, 0x7f, 0x1f, 0x0f, 0xc9, 0x35,
yading@11:     // RTCP index
yading@11:     0x80, 0x00, 0x00, 0x03,
yading@11:     // HMAC
yading@11:     0xe9, 0x3b, 0xc0, 0x5c, 0x0c, 0x06, 0x9f, 0xab, 0xc0, 0xde,
yading@11: };
yading@11: 
yading@11: static const char *aes128_32_key = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmn";
yading@11: 
yading@11: static const uint8_t rtp_aes128_32[] = {
yading@11:     // RTP header
yading@11:     0x80, 0xe0, 0x12, 0x34, 0x12, 0x34, 0x56, 0x78, 0x12, 0x34, 0x56, 0x78,
yading@11:     // encrypted payload
yading@11:     0x62, 0x69, 0x76, 0xca, 0xc5,
yading@11:     // HMAC
yading@11:     0xa1, 0xac, 0x1b, 0xb4,
yading@11: };
yading@11: 
yading@11: static const uint8_t rtcp_aes128_32[] = {
yading@11:     // RTCP header
yading@11:     0x81, 0xc9, 0x00, 0x07, 0x12, 0x34, 0x56, 0x78,
yading@11:     // encrypted payload
yading@11:     0x35, 0xe9, 0xb5, 0xff, 0x0d, 0xd1, 0xde, 0x70, 0x74, 0x10, 0xaa, 0x1b,
yading@11:     0xb2, 0x8d, 0xf0, 0x20, 0x02, 0x99, 0x6b, 0x1b, 0x0b, 0xd0, 0x47, 0x34,
yading@11:     // RTCP index
yading@11:     0x80, 0x00, 0x00, 0x04,
yading@11:     // HMAC
yading@11:     0x5b, 0xd2, 0xa9, 0x9d,
yading@11: };
yading@11: 
yading@11: static const char *aes128_80_32_key = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmn";
yading@11: 
yading@11: static const uint8_t rtp_aes128_80_32[] = {
yading@11:     // RTP header
yading@11:     0x80, 0xe0, 0x12, 0x34, 0x12, 0x34, 0x56, 0x78, 0x12, 0x34, 0x56, 0x78,
yading@11:     // encrypted payload
yading@11:     0x62, 0x69, 0x76, 0xca, 0xc5,
yading@11:     // HMAC
yading@11:     0xa1, 0xac, 0x1b, 0xb4,
yading@11: };
yading@11: 
yading@11: static const uint8_t rtcp_aes128_80_32[] = {
yading@11:     // RTCP header
yading@11:     0x81, 0xc9, 0x00, 0x07, 0x12, 0x34, 0x56, 0x78,
yading@11:     // encrypted payload
yading@11:     0xd6, 0xae, 0xc1, 0x58, 0x63, 0x70, 0xc9, 0x88, 0x66, 0x26, 0x1c, 0x53,
yading@11:     0xff, 0x5d, 0x5d, 0x2b, 0x0f, 0x8c, 0x72, 0x3e, 0xc9, 0x1d, 0x43, 0xf9,
yading@11:     // RTCP index
yading@11:     0x80, 0x00, 0x00, 0x05,
yading@11:     // HMAC
yading@11:     0x09, 0x16, 0xb4, 0x27, 0x9a, 0xe9, 0x92, 0x26, 0x4e, 0x10,
yading@11: };
yading@11: 
yading@11: static void print_data(const uint8_t *buf, int len)
yading@11: {
yading@11:     int i;
yading@11:     for (i = 0; i < len; i++)
yading@11:         printf("%02x", buf[i]);
yading@11:     printf("\n");
yading@11: }
yading@11: 
yading@11: static int test_decrypt(struct SRTPContext *srtp, const uint8_t *in, int len,
yading@11:                         uint8_t *out)
yading@11: {
yading@11:     memcpy(out, in, len);
yading@11:     if (!ff_srtp_decrypt(srtp, out, &len)) {
yading@11:         print_data(out, len);
yading@11:         return len;
yading@11:     } else
yading@11:         return -1;
yading@11: }
yading@11: 
yading@11: static void test_encrypt(const uint8_t *data, int in_len, const char *suite,
yading@11:                          const char *key)
yading@11: {
yading@11:     struct SRTPContext enc = { 0 }, dec = { 0 };
yading@11:     int len;
yading@11:     char buf[RTP_MAX_PACKET_LENGTH];
yading@11:     ff_srtp_set_crypto(&enc, suite, key);
yading@11:     ff_srtp_set_crypto(&dec, suite, key);
yading@11:     len = ff_srtp_encrypt(&enc, data, in_len, buf, sizeof(buf));
yading@11:     if (!ff_srtp_decrypt(&dec, buf, &len)) {
yading@11:         if (len == in_len && !memcmp(buf, data, len))
yading@11:             printf("Decrypted content matches input\n");
yading@11:         else
yading@11:             printf("Decrypted content doesn't match input\n");
yading@11:     } else {
yading@11:         printf("Decryption failed\n");
yading@11:     }
yading@11:     ff_srtp_free(&enc);
yading@11:     ff_srtp_free(&dec);
yading@11: }
yading@11: 
yading@11: int main(void)
yading@11: {
yading@11:     static const char *aes128_80_suite = "AES_CM_128_HMAC_SHA1_80";
yading@11:     static const char *aes128_32_suite = "AES_CM_128_HMAC_SHA1_32";
yading@11:     static const char *aes128_80_32_suite = "SRTP_AES128_CM_HMAC_SHA1_32";
yading@11:     static const char *test_key = "abcdefghijklmnopqrstuvwxyz1234567890ABCD";
yading@11:     uint8_t buf[RTP_MAX_PACKET_LENGTH];
yading@11:     struct SRTPContext srtp = { 0 };
yading@11:     int len;
yading@11:     ff_srtp_set_crypto(&srtp, aes128_80_suite, aes128_80_key);
yading@11:     len = test_decrypt(&srtp, rtp_aes128_80, sizeof(rtp_aes128_80), buf);
yading@11:     test_encrypt(buf, len, aes128_80_suite, test_key);
yading@11:     test_encrypt(buf, len, aes128_32_suite, test_key);
yading@11:     test_encrypt(buf, len, aes128_80_32_suite, test_key);
yading@11:     test_decrypt(&srtp, rtcp_aes128_80, sizeof(rtcp_aes128_80), buf);
yading@11:     test_encrypt(buf, len, aes128_80_suite, test_key);
yading@11:     test_encrypt(buf, len, aes128_32_suite, test_key);
yading@11:     test_encrypt(buf, len, aes128_80_32_suite, test_key);
yading@11:     ff_srtp_free(&srtp);
yading@11: 
yading@11:     memset(&srtp, 0, sizeof(srtp)); // Clear the context
yading@11:     ff_srtp_set_crypto(&srtp, aes128_32_suite, aes128_32_key);
yading@11:     test_decrypt(&srtp, rtp_aes128_32, sizeof(rtp_aes128_32), buf);
yading@11:     test_decrypt(&srtp, rtcp_aes128_32, sizeof(rtcp_aes128_32), buf);
yading@11:     ff_srtp_free(&srtp);
yading@11: 
yading@11:     memset(&srtp, 0, sizeof(srtp)); // Clear the context
yading@11:     ff_srtp_set_crypto(&srtp, aes128_80_32_suite, aes128_80_32_key);
yading@11:     test_decrypt(&srtp, rtp_aes128_80_32, sizeof(rtp_aes128_80_32), buf);
yading@11:     test_decrypt(&srtp, rtcp_aes128_80_32, sizeof(rtcp_aes128_80_32), buf);
yading@11:     ff_srtp_free(&srtp);
yading@11:     return 0;
yading@11: }
yading@11: #endif /* TEST */